1. Field of the Invention
The present invention relates generally to environmental control of storage buildings and facilities. More particularly, the present invention relates to the control of such parameters as temperature, humidity, and carbon dioxide (CO2) within a storage facility wherein produce or like commodities are stored.
2. State of the Art
Produce providers often desire to store fruits and vegetables for extended periods of time. Produce is often stored to maintain adequate supplies during periods when a particular commodity is out of season. Processors of fruit and vegetables increasingly desire commercial growers to store their products for longer and longer periods of time. Indeed, processors require a year-round supply of produce while requiring that the quality of such produce remain high.
To store produce for extended periods of time without substantial degradation of quality, it becomes imperative to control the environment in which the produce is stored. Control of the storage facility environment may include the control of, for example, temperature, humidity, and air quality including carbon dioxide (CO2) content. Typically, control of such parameters in a storage facility environment entails movement of air within the facility. Oftentimes, this includes introduction of air from outside the facility. Other times it may simply involve the circulation of existing air inside the storage facility.
One method of controlling the environment has been to place fans or air-handling units in the facility The fans may be turned on when the temperature rises above a predetermined upper level and shut off when the temperature of the facility reaches a predetermined lower level. A system of this type is described in U.S. Pat. No. 3,801,888 to Faulkner. This type of system utilizes the fans at full power, allowing them to cool the facility at a relatively quick pace, but also allowing temperatures or other environmental parameters to change rapidly within a specified range. Rapid changes in temperature or temperature spikes may often cause a temperature-induced shock to the stored inventory, ultimately resulting in quality degradation. Similarly, rapid changes in other environmental parameters may degrade the quality of the stored commodity.
Some systems have sought to utilize multi-speed fans such as is described in U.S. Pat. No. 3,896,359 to Olander et al. Such a system is implemented with the desire of allowing temperature or other environmental changes to take place at a slower rate. However, even these systems do not allow the desired flexibility in controlling a chosen environmental parameter within the storage facility. Such systems employ low- and high-speed control of the fan or air-handling unit. While this allows for a stepped transition from one temperature to another, it simply reduces the magnitude of any temperature spike rather than providing a continuous control of temperature within the storage facility. This is because the high- and low-speed settings each correspond to a defined range of operability. Thus, for example, in controlling temperature, the fans will remain inoperative if the temperature of the facility is within a defined temperature range. The fans will then operate at a low-speed setting once the temperature increases into a second defined range. Finally, the fans will operate at a high-speed setting if the temperature increases into a third defined range. The process will reverse itself as the temperature decreases. However, the ranges cannot be defined too tightly, otherwise the far. will be constantly starting and stopping as the temperature fluctuates between the first and second range. On the other hand, the defined ranges may not be set too broadly. If the ranges are too broad, then the temperature will increase to the point where the fans will be operating at the high-speed setting for extended periods of time in an attempt to bring the temperature back to an acceptable value. Also, depending on the commodity being stored, broad parameter ranges may simply not be acceptable from a quality standpoint.
Another important consideration. in the environmental control of a storage facility is the efficient use of power. With most systems relying on fans that are cycled between on and off positions, or those systems having high/low-speed settings, power consumption is of paramount concern to the facility operator. Storing commodities for extended periods of time requires a significant consumption of power with existing systems and methods. The cost of such power, while initially resting with the facility operator, ultimately gets passed along to the consumer in the form of higher prices at the market. Thus, an efficient and accurate environmental control system for storage facilities would be of benefit to more than just the facility operator.
In view of the shortcomings in the art, it would be advantageous to provide an environmental control system for a storage facility which effectively controls specified environmental parameters while consuming a reduced amount of energy. Such a system or method should be simple to employ in existing as well as new storage facilities.
In accordance with one aspect of the invention, a method is provided for controlling the internal environment of a storage facility, such as a storage bin for produce. The method includes the steps of providing a fan, or a plurality of fans, for moving the internal air of the storage facility. The fans are continuously operated within the storage facility The fans may be operated continuously at a speed which is below their full capacity for continuous parameter control and reduced power consumption. The system monitors a parameter indicative of the internal environment of the storage facility. For example, a temperature sensor may be employed to monitor the internal temperature of the storage facility. Once the temperature has been monitored, the speed of the fans is altered accordingly. If the internal temperature needs to be reduced, then the fans may be operated at a higher rotational speed, increasing the air movement within the storage facility. Likewise, if the air temperature needs to be increased, the fan speeds will again be altered to accomplish this requirement. The same method may be applied in monitoring other parameters and changing the rate of air flow to obtain a desired value for the given parameter
Additionally, environmental parameters outside of the storage facility may be monitored to assist in the regulation of airflow inside the storage facility. For example, outside air temperature may be monitored and compared to the desired facility temperature to determine whether outside air should be admitted into the facility via a ventilation inlet. Various restrictions may be placed on the admittance of outside air, such as prohibiting outside air into the facility if the outside temperature is above a specified maximum or below a specified minimum.
In accordance with another aspect of the present invention, a system is provided for controlling the internal environment of a storage facility. The system includes a fan or multiple fans which are adapted to operate continuously. The fans may be operated continuously at a speed which is below their operational capacity. The fans are placed to move the internal air of the storage facility during operation. Each fan is coupled to a variable speed drive for controlling the operational speed of the fans. At least one sensor is employed to monitor one or more internal environmental parameters of the storage facility such as temperature, humidity, gas levels, or chemical levels. The sensor is coupled to an electronic control unit which is also coupled to the variable speed drive. The sensor provides a signal to the electronic control unit, the signal representing a measured value of an internal environmental parameter. The electronic control unit then provides a signal to the variable speed drive based upon the sensed parameter causing the associated fan to vary in speed accordingly.
Additional elements may be configured with the system to render greater control and flexibility. For example, sensors monitoring an external environment may be coupled to the electronic control unit to assist in determining fan speed. Ventilation inlets or outlets may also be coupled to the electronic control unit for controlling flow of air into and out of the facility, respectively.